Types of ceramic capacitors. What is a capacitor

When assembling homemade electronic circuits, you are inevitably faced with the selection of the necessary capacitors.

Moreover, to assemble the device, you can use capacitors that have already been used and have worked for some time in electronic equipment.

Naturally, before reuse, it is necessary to check capacitors, especially electrolytic ones, which are more susceptible to aging.

When selecting capacitors of constant capacity, it is necessary to understand the markings of these radio elements, otherwise, if there is an error, the assembled device will either refuse to work correctly or will not work at all. The question arises, how to read the capacitor markings?

A capacitor has several important parameters that should be taken into account when using them.

The first thing is rated capacitance. It is measured in fractions of Farad.

The second is permission. Or in another way permissible deviation of nominal capacity from the specified one. This parameter is rarely taken into account, since household radio equipment uses radio elements with a tolerance of up to ±20%, and sometimes more. It all depends on the purpose of the device and the features of a particular device. This parameter is usually not indicated on circuit diagrams.

The third thing indicated in the labeling is permissible operating voltage. This is a very important parameter and you should pay attention to it if the capacitor will be used in high-voltage circuits.

So, let's figure out how capacitors are marked.

Some of the most popular capacitors that can be used are constant capacitors K73 - 17, K73 - 44, K78 - 2, ceramic KM-5, KM-6 and the like. Analogs of these capacitors are also used in imported electronic equipment. Their labeling differs from domestic ones.

Domestic-made capacitors K73-17 are polyethylene terephthalate film protected capacitors. The housing of these capacitors is marked with an alphanumeric index, for example 100nJ, 330nK, 220nM, 39nJ, 2n2M.

K73 series capacitors and their markings

Labeling rules.

Capacitances from 100 pF to 0.1 µF are marked in nanofarads, indicating the letter H or n.

Designation 100 n is the value of the nominal capacity. For 100n - 100 nanofarads (nF) - 0.1 microfarads (uF). Thus, a capacitor with index 100n has a capacity of 0.1 μF. Similar for other notations. For example:
330n – 0.33 µF, 10n – 0.01 µF. For 2n2 – 0.0022 µF or 2200 picofarads (2200 pF).

You can find markings like 47 H C. This entry corresponds to 47 n K and is 47 nanofarads or 0.047 µF. Similar to 22NS - 0.022 µF.

In order to easily determine the capacity, you need to know the designations of the main submultiple units - milli, micro, nano, pico and their numerical values. Read more about this.

Also in the marking of K73 capacitors there are such designations as M47C, M10C.
Here, letter M conventionally means microfarad. The value 47 comes after M, i.e. the nominal capacitance is a fraction of a microfarad, i.e. 0.47 µF. For M10C - 0.1 µF. It turns out that capacitors marked M10C and 100nJ have the same capacity. The only differences are in the recording.

Thus, capacitance from 0.1 µF and above is indicated with the letter M, m Instead of a decimal point, the leading zero is omitted.

The nominal capacity of domestic capacitors up to 100 pF is indicated in picofarads, putting the letter P or p after the number. If the capacitance is less than 10 pF, then put the letter R and two numbers. For example, 1R5 = 1.5 pF.

On ceramic capacitors (type KM5, KM6), which are small in size, usually only a numerical code is indicated. Here, look at the photo.

Ceramic capacitors with capacitance marked with a numerical code

For example, numerical marking 224 corresponds to value 22 0000 picofarad, or 220 nanofarad and 0.22 µF. In this case, 22 is the numerical value of the denomination value. The number 4 indicates the number of zeros. The result the number is the capacitance value in picofarads. Writing 221 means 220 pF, and writing 220 means 22 pF. If the marking uses a four-digit code, then the first three digits are the numerical value of the denomination value, and the last, fourth, is the number of zeros. So at 4722, the capacitance is 47200 pF - 47.2 nF. I think we've sorted this out.

The permissible deviation of the capacity is marked either with a percentage number (±5%, 10%, 20%) or with a Latin letter. Sometimes you can find the old tolerance designation encoded with a Russian letter. The permissible deviation of capacitance is similar to the tolerance for the resistance value of resistors.

Letter code of capacity deviation (tolerance).

So, if a capacitor with the following marking is M47C, then its capacity is 0.047 μF, and the tolerance is ±10% (according to the old marking with a Russian letter). It is quite difficult to find a capacitor with a tolerance of ±0.25% (as marked with a Latin letter) in household equipment, which is why a value with a larger error was chosen. Mainly, capacitors with approval are widely used in household equipment. H, M, J, K. The letter indicating the tolerance is indicated after the value of the nominal capacity, like this 22n K, 220n M, 470n J.

Table for deciphering the conditional letter code of the permissible deviation of the capacity.

Marking of capacitors by operating voltage.

An important parameter of the capacitor is also the permissible operating voltage. It should be taken into account when assembling homemade electronics and repairing household radio equipment. For example, when repairing compact fluorescent lamps, it is necessary to select a capacitor for the appropriate voltage when replacing failed ones. It would be a good idea to take a capacitor with a margin of operating voltage.

Typically, the value of the permissible operating voltage is indicated after the rated capacity and tolerance. It is designated in volts with the letter B (old marking) and V (new). For example, like this: 250V, 400V, 1600V, 200V. In some cases, the V is omitted.

Sometimes Latin letter coding is used. To decipher, you should use the table of letter coding of the operating voltage.

Thus, we learned how to determine the capacitance of a capacitor by marking, and along the way we became acquainted with its main parameters.

The marking of imported capacitors is different, but largely corresponds to what is described.

Content:

A capacitor is a device capable of storing electrical charges. It is used in electrical and electronic circuits everywhere. Modern industry produces many types of them, which differ from each other in different parameters. This is the capacity, principle of operation, type of separation of charging conductors, range of permissible voltages, layout, materials from which the device is made.

Any capacitor consists of two conductors separated by an insulator. Since charging a capacitor is the introduction of charged particles onto these conductors, one conductor of one sign and the other of another, and the charges will be held by the force of mutual attraction, the efficiency depends on this force. The closer the conductors are to each other and the larger their “almost touching” area, the larger it is. The medium separating the conductors also makes its contribution. This medium is a dielectric having a certain dielectric constant.

d – thickness of the dielectric separating the metal plates

The capacitance of the capacitor is calculated by the formula

Where S is the area of ​​the plates, d is the thickness of the dielectric (the distance between the plates), and ε is the permeability of the dielectric used relative to vacuum, the dielectric constant of which is known quite accurately:

Here it is expressed through other SI units. Here there are meters cubed in the denominator, and seconds to the fourth power in the numerator, which comes from the formula where the denominator is the speed of light squared. And then the capacitance C is measured in farads.

And from the formula it is clear that the capacitance depends precisely on the area of ​​the plates, the distance between them (which is filled with a dielectric) and the dielectric material, the value of ε of which can be found in the tables. Capacitors are classified according to type of use and type of component.

Classification by principle of action

The simplest capacitor is also called dry, or solid-state, because all its materials are solid and very ordinary. Knowing the description, it can be made manually. Paper tape is used as an insulator, but since it is hygroscopic, it is impregnated with paraffin or oil.

Dry capacitors

Dry or wet capacitors - depends on the filling between the plates. For dry ones, it can be paper, ceramics, mica, plastic (polyester, polypropylene). Each dielectric has its own physical properties. The most durable (ceramics) resist physical destruction and breakdown well. Plastic ones allow coatings to be applied in the form of metal spraying directly onto the dielectric layer, which allows one to follow the path of microminiaturization.

Types of capacitors with other component states

In addition to solid dielectric, there are capacitors with dielectric:

• liquid;

• gaseous (filled with inert gas to protect the electrodes);

• vacuum;

• air.

However, electrodes are not always completely solid.

Electrolytic capacitors

To create a large capacity, methods of bringing the plates together are used, not mechanical, but chemical. Taking advantage of the fact that aluminum foil is always covered in air with a layer of dielectric (Al 2 O 3), a liquid electrode in the form of an electrolyte is brought very close to the aluminum electrode. Then the thickness of the insulating gap is calculated in atomic distances, and this dramatically increases the capacitance.

d – dielectric thickness

Since there is a layer of oxide, a dielectric, on the lower surface of the upper plate, it is precisely its thickness that should be considered d - the thickness of the dielectric. The bottom electrode is the bottom plate, plus a layer of electrolyte with which the paper is impregnated.

In electrolytic capacitors, the charge is created not only by free electrons of the metal, but also by electrolyte ions. Therefore, the polarity of the connection is important.

In addition to electrolytic capacitors that use metal oxide as insulation, field-effect (MOS) transistors operate on the same principle. They are often used in electronic circuits as capacitors with a capacity of several tens of nanofarads.

Another similar operating principle is used by oxide-semiconductor capacitors, in which instead of a liquid electrolyte there is a solid semiconductor. But these types do not exhaust capacitors, the dielectric layer of which has a microscopic thickness.

Supercapacitor or ionistor

Another option is to create a layer that plays the role of a dielectric in a liquid electrolyte. If you pour it on the surface of a certain porous conductor (activated carbon), then if there is a charge on it, ions of the opposite sign from the electrolyte “stick” to the conductor. And they, in turn, are joined by other ions. And everything together forms a multilayer structure capable of accumulating electrical charges.

The processes in a liquid electrolyte of a special composition for supercapacitors already resemble something that happens in battery electrolytes. The ionistor's characteristics are similar to those of batteries; in addition, its charging is easier and faster. And in them, during charging/discharging cycles, the electrodes do not deteriorate, as is usually the case in batteries. Ionistors are more reliable, durable, and they are used as power devices in electric vehicles. And the porous substance of the electrodes provides simply a colossal surface area. Together with the nanoscopically small thickness of the insulating layer in the electrolyte, this creates the gigantic capacity of supercapacitors (ultracapacitors) - farads, tens and hundreds of farads. There are many different supercapacitors available, some of which look no different from batteries.

Classification by application

Most capacitors are manufactured for use in fine-tuned electrical circuits and circuits. But in many circuits, electrical or frequency parameters are adjusted. Capacitors are very convenient for this purpose: you can change the capacitance without changing the electrical contacts between the plates.

According to this feature, capacitors are constant, variable and tuning.

Trimmers are usually designed in miniature form and are designed for permanent operation in circuits after a small preliminary optimizing adjustment. Variables have wider ranges of parameters to allow for systematic tuning (for example, searching for a wave in a radio receiver).

By voltage range

The operating voltage range is a very important characteristic of a capacitor. In electronic circuits, voltages are usually small. The upper limit is about 100 volts. But power supply circuits, various power supplies, rectifiers, device stabilizers require the installation of capacitors that could withstand voltages up to 400–500 volts - taking into account possible surges, and even up to 1000 volts.

But in electricity transmission networks the voltages are much higher. There are high-voltage capacitors of special design.

Using a capacitor outside its voltage range risks breakdown. After a breakdown, the device becomes simply a conductor and ceases to perform its functions. This is especially dangerous where a capacitor is installed to decouple circuits by current, separating the DC voltage from the AC component. In this case, a breakdown threatens that part of the circuit where constant voltage will then flow: other elements may burn, and there may be an electric shock. For electrolytic capacitors, this phenomenon also threatens an explosion.

Left – up to 35 kV, right – up to 4 kV

Since breakdown at high voltage requires a certain minimum distance between conductors, devices for high-voltage versions are usually made of significant size. Or they are made of certain breakdown-resistant materials: ceramic and... metal-paper. Of course, everything is in a housing that has the appropriate properties.

Capacitor markings

There are several markings. The old marking may consist of three or four digits, in which case the first two (three) digits indicate the mantissa of the capacitance (in picofarads), the last digit gives the power of the tens factor.

This is what the three-digit marking of capacitors looks like (designation of capacitances)

As you can see, this marking only covers the capacitance of capacitors.

Code marking contains information about materials, stresses, and tolerances.

On large capacitors, the designations are located directly on the body.

If there are no voltage markings, this is a low voltage device. There are conventional letter designations for voltages.

Polarity is indicated by “+ -” or a ring-shaped groove near the negative terminal. If this symbol is present, please strictly observe the polarity!

Capacitors(from Latin condenso - compact, thicken) - these are radioelements with concentrated electrical capacitance formed by two or more electrodes (plates) separated by a dielectric (special thin paper, mica, ceramics, etc.). The capacitance of the capacitor depends on the size (area) of the plates, the distance between them and the properties of the dielectric.

An important property of a capacitor is that for alternating current it represents resistance, the value of which decreases with increasing frequency.

The main units for measuring the capacitance of capacitors are: Farad, microFarad, nanoFarad, picofarad, the designations on capacitors for which look like: F, μF, nF, pF.

Like resistors, capacitors are divided into capacitors of constant capacitance, capacitors of variable capacitance (VCA), tuning and self-regulating capacitors. The most common are fixed capacitors.

They are used in oscillating circuits, various filters, as well as for separating DC and AC circuits and as blocking elements.

Fixed capacitors

The conventional graphic designation of a constant-capacity capacitor—two parallel lines—symbolizes its main parts: two plates and a dielectric between them (Fig. 1).

Rice. 1. Fixed capacitors and their designation.

Near the capacitor designation on the diagram, its rated capacitance and sometimes its rated voltage are usually indicated. The basic unit of capacitance is the farad (F) - the capacitance of such an isolated conductor, the potential of which increases by one volt with an increase in charge by one coulomb.

This is a very large value, which is not used in practice. In radio engineering, capacitors with capacities ranging from fractions of a picofarad (pF) to tens of thousands of microfarads (μF) are used. Recall that 1 µF is equal to one millionth of a farad, and 1 pF is one millionth of a microfarad or one trillionth of a farad.

According to GOST 2.702-75, the nominal capacitance from 0 to 9,999 pF is indicated on the circuits in picofarads without designating the unit of measurement, from 10,000 pF to 9,999 μF - in microfarads with the designation of the unit of measurement by the letters mk (Fig. 2).

Rice. 2. Designation of units of measurement for capacitance of capacitors in the diagrams.

Capacitance designation on capacitors

The rated capacitance and the permissible deviation from it, and in some cases the rated voltage, are indicated on the capacitor housings.

Depending on their size, the nominal capacity and permissible deviation are indicated in full or abbreviated (coded) form.

The full designation of capacitance consists of the corresponding number and unit of measurement, and, as in the diagrams, capacitance from 0 to 9,999 pF is indicated in picofarads (22 pF, 3,300 pF, etc.), and from 0.01 to 9,999 µF - in microfarads (0.047 µF, 10 µF, etc.).

In abbreviated marking, the units of measurement of capacitance are designated by the letters P (picofarad), M (microfarad) and N (nanofarad; 1 nano-farad = 1000 pF = 0.001 μF).

At the same time Capacitance from 0 to 100 pF is indicated in picofarads, placing the letter P either after the number (if it is an integer) or in place of the decimal point (4.7 pF - 4P7; 8.2 pF - 8P2; 22 pF - 22P; 91 pF - 91P, etc.).

Capacitance from 100 pF (0.1 nF) to 0.1 µF (100 nF) is indicated in nanofarads, and from 0.1 µF and above - in microfarads.

In this case, if the capacitance is expressed in fractions of a nanofarad or microfarad, the corresponding the unit of measurement is placed in place of zero and comma(180 pF = 0.18 nF - H18; 470 pF = 0.47 nF - H47; 0.33 µF - MZZ; 0.5 µF - MbO, etc.), and if the number consists of an integer part and a fraction - at the decimal point (1500 pF = 1.5 nF - 1H5; 6.8 µF - 6M8, etc.).

Capacitances of capacitors, expressed as an integer number of corresponding units of measurement, are indicated in the usual way (0.01 μF - 10N, 20 μF - 20M, 100 μF - 100M, etc.). To indicate the permissible deviation of capacitance from the nominal value, the same coded designations are used as for resistors.

Features and requirements for capacitors

Depending on the circuit in which capacitors are used, different requirements apply to them. requirements. Thus, a capacitor operating in an oscillating circuit must have low losses at the operating frequency, high stability of capacitance over time and with changes in temperature, humidity, pressure, etc.

Capacitor losses, determined mainly by losses in the dielectric, increase with increasing temperature, humidity and frequency. Capacitors with a dielectric made of high-frequency ceramics, with mica and film dielectrics have the lowest losses, while capacitors with a paper dielectric and ferroelectric ceramics have the highest losses.

This circumstance must be taken into account when replacing capacitors in radio equipment. A change in capacitance of a capacitor under the influence of the environment (mainly its temperature) occurs due to changes in the dimensions of the plates, the gaps between them and the properties of the dielectric.

Depending on the design and dielectric used, capacitors are characterized by different temperature coefficient of the container(TKE), which shows the relative change in capacitance with a change in temperature by one degree; TKE can be positive or negative. Based on the value and sign of this parameter, capacitors are divided into groups, which are assigned the corresponding letter designations and body color.

To maintain the tuning of oscillatory circuits when operating over a wide temperature range, they often use series and parallel connections of capacitors in which TKE have different signs. Due to this, when the temperature changes, the tuning frequency of such a temperature-compensated circuit remains practically unchanged.

Like any conductors, capacitors have some inductance. It is larger, the longer and thinner the leads of the capacitor, the larger the size of its plates and internal connecting conductors.

They have the highest inductance paper capacitors, in which the facings are made in the form of long strips of foil, rolled together with the dielectric into a round or other shaped roll. Unless special measures are taken, such capacitors do not perform well at frequencies above a few megahertz.

Therefore, in practice, to ensure the operation of a blocking capacitor in a wide frequency range, a ceramic or mica capacitor of small capacity is connected in parallel to the paper capacitor.

However, there are paper capacitors with low self-inductance. In them, strips of foil are connected to the terminals not in one, but in many places. This is achieved either by strips of foil inserted into the roll during winding, or by moving the strips (linings) to opposite ends of the roll and soldering them (Fig. 1).

Feed-through and reference capacitors

To protect against interference that can penetrate into the device through the power supply circuits and vice versa, as well as for various interlocks, so-called pass capacitors. Such a capacitor has three terminals, two of which are a solid current-carrying rod passing through the capacitor body.

One of the capacitor plates is attached to this rod. The third terminal is a metal body to which the second plate is connected. The body of the pass-through capacitor is fixed directly to the chassis or screen, and the current-carrying wire (power circuit) is soldered to its middle terminal.

Thanks to this design, high-frequency currents are short-circuited to the chassis or screen of the device, while direct currents pass unimpeded.

Used at high frequencies ceramic feed-through capacitors, in which the role of one of the plates is played by the central conductor itself, and the other is the metallization layer deposited on the ceramic tube. These design features are also reflected by the conventional graphic designation of the feed-through capacitor (Fig. 3).

Rice. 3. Appearance and image on the diagrams of feed-through and support capacitors.

The outer lining is designated either in the form of a short arc (a), or in the form of one (b) or two (c) straight line segments with leads from the middle. The last designation is used when depicting a pass-through capacitor in the screen wall.

For the same purpose as checkpoints, they are used reference capacitors, which are a kind of mounting racks mounted on a metal chassis. The plate connected to it is distinguished in the designation of such a capacitor by three inclined lines, symbolizing “grounding” (Fig. 3d).

Oxide capacitors

To operate in the audio frequency range, as well as to filter rectified supply voltages, capacitors are needed, the capacitance of which is measured in tens, hundreds and even thousands of microfarads.

Such capacity with sufficiently small dimensions has oxide capacitors(old name - electrolytic). In them, the role of one plate (anode) is played by an aluminum or tantalum electrode, the role of a dielectric is played by a thin oxide layer deposited on it, and the role of the other plate (cathode) is a special electrolyte, the output of which is often the metal body of the capacitor.

Unlike others most types of oxide capacitors are polar, i.e., they require a polarizing voltage for normal operation. This means that they can only be turned on in DC or pulsating voltage circuits and only in the polarity (cathode to minus, anode to plus) indicated on the housing.

Failure to comply with this condition leads to failure of the capacitor, which is sometimes accompanied by an explosion!

Oxide capacitor switching polarity are shown in the diagrams with a “+” sign, depicted near the plate that symbolizes the anode (Fig. 4, a).

This is the general designation for a polarized capacitor. Along with it, specifically for oxide capacitors, GOST 2.728-74 established a symbol in which the Positive plate is depicted as a narrow rectangle (Fig. 4.6), and the “+” sign can be omitted in this case.

Rice. 4. Oxide capacitors and their designation on circuit diagrams.

In circuits of radio-electronic devices, you can sometimes find the designation of an oxide capacitor in the form of two narrow rectangles (Fig. 4, c). This is a symbol of a non-polar oxide capacitor that can operate in alternating current circuits (i.e. without polarizing voltage).

Oxide capacitors are very sensitive to overvoltage, so diagrams often indicate not only their rated capacitance, but also their rated voltage.

In order to reduce the size, two capacitors are sometimes placed in one housing, but only three leads are made (one is common). The symbol of a dual capacitor clearly conveys this idea (Fig. 4d).

Variable capacitors (VCA)

Variable capacitor consists of two groups of metal plates, one of which can move smoothly in relation to the other. During this movement, the plates of the moving part (rotor) are usually inserted into the gaps between the plates of the stationary part (stator), as a result of which the area of ​​overlap of one plate by another, and therefore the capacitance, changes.

Dielectric In the KPI, air is most often used. In small-sized equipment, for example, in transistor pocket receivers, CPE with a solid dielectric, which is used as films of wear-resistant high-frequency dielectrics (fluoroplastic, polyethylene, etc.), are widely used.

The parameters of PCBs with a solid dielectric are somewhat worse, but they are much cheaper to produce and their dimensions are much smaller than PCBs with an air dielectric.

We have already met the symbol KPI - this is the symbol of a constant-capacity capacitor crossed out by a regulation sign. However, from this designation it is not clear which of the plates symbolizes the rotor and which symbolizes the stator. To show this in the diagram, the rotor is depicted as an arc (Fig. 5).

Rice. 5. Designation of variable capacitors.

The main parameters of the KPI, which allow us to evaluate its capabilities when operating in an oscillating circuit, are the minimum and maximum capacitance, which, as a rule, are indicated on the diagram next to the KPI symbol.

In most radio receivers and radio transmitters, KPI blocks consisting of two, three or more sections are used to simultaneously tune several oscillatory circuits.

The rotors in such blocks are mounted on one common shaft, by rotating which you can simultaneously change the capacity of all sections. The outer plates of the rotors are often split (along the radius). This allows you to adjust the unit at the factory so that the capacities of all sections are the same in any position of the rotor.

The capacitors included in the KPI block are shown separately in the diagrams. To show that they are combined into a block, i.e., controlled by one common handle, arrows indicating regulation are connected by a dashed line of mechanical connection, as shown in Fig. 6.

Rice. 6. Designation of dual variable capacitors.

When depicting the block's KPIs in different parts of the diagram that are far apart from one another, the mechanical connection is not shown, limiting itself only to the corresponding numbering of sections in the position designation (Fig. 6, sections C 1.1, C 1.2 and C 1.3).

In measuring equipment, for example in the arms of capacitive bridges, so-called differential capacitors(from Latin differentia - difference).

They have two groups of stator and one rotor plates, arranged so that when the rotor plates exit the gaps between the plates of one stator group, they at the same time enter between the plates of the other.

In this case, the capacitance between the plates of the first stator and the rotor plates decreases, and between the plates of the rotor and the second stator increases. The total capacitance between the rotor and both stators remains unchanged. Such capacitors are depicted in diagrams, as shown in Fig. 7.

Rice. 7. Differential capacitors and their designation on the diagrams.

Trimmer capacitors. To set the initial capacitance of the oscillating circuit, which determines the maximum frequency of its tuning, tuning capacitors are used, the capacitance of which can be changed from a few picofarads to several tens of picofarads (sometimes more).

The main requirement for them is a smooth change in capacity and reliable fixation of the rotor in the position set during adjustment. The axes of trimming capacitors (usually short) have a slot, so adjusting their capacitance is only possible using a tool (screwdriver). In broadcasting equipment, capacitors with a solid dielectric are most widely used.

Rice. 8. Trimmer capacitors and their designation.

The design of a ceramic trimmer capacitor (CTC) of one of the most common types is shown in Fig. 8, a. It consists of a ceramic base (stator) and a ceramic disk (rotor) movably mounted on it.

The capacitor plates—thin layers of silver—are applied by burning onto the stator and the outside of the rotor. The capacity is changed by rotating the rotor. In the simplest equipment, wire tuning capacitors are sometimes used.

Such an element consists of a piece of copper wire with a diameter of 1 ... 2 and a length of 15 ... 20 mm, on which an insulated wire with a diameter of 0.2 ... 0.3 mm is wound tightly, turn to turn (Fig. 8, b). The container is changed by unwinding the wire, and to prevent the winding from slipping, it is impregnated with some kind of insulating compound (varnish, glue, etc.).

Trimmer capacitors denoted on the diagrams by the main symbol crossed out by the tuning control sign (Fig. 8, c).

Self-regulating capacitors

Using special ceramics as a dielectric, the dielectric constant of which strongly depends on the electric field strength, you can obtain a capacitor whose capacitance depends on the voltage on its plates.

Such capacitors are called varicondas(from the English words vari (able) - variable and cond (enser) - capacitor). When the voltage changes from a few volts to the nominal value, the capacitance of the variconde changes by 3-6 times.

Rice. 9. Varicond and its designation on the diagrams.

Varicondas can be used in various automation devices, in swing frequency generators, modulators, for electrical adjustment of oscillatory circuits, etc.

Symbol for variconda— capacitor symbol with the sign of nonlinear self-regulation and the Latin letter U (Fig. 9, a).

The designation of thermal capacitors used in electronic wristwatches is constructed in a similar way. The factor that changes the capacitance of such a capacitor—the temperature of the medium—is designated by the symbol t° (Fig. 9, b). However, what is a capacitor is often searched for

Literature: V.V. Frolov, Language of radio circuits, Moscow, 1998.

There are many different types of capacitors on the electronic components market today, and each type has its own advantages and disadvantages. Some are capable of operating at high voltages, others have significant capacitance, others have low self-inductance, and some are characterized by extremely low leakage current. All these factors determine the applications of specific types of capacitors.

Let's look at what types of capacitors there are. In general, there are a lot of them, but here we will look at the main popular types of capacitors and figure out how to determine this type.

For example, K50-35 or K50-29, consist of two thin strips of aluminum, twisted into a roll, between which electrolyte-impregnated paper is placed as a dielectric. The roll is placed in a sealed aluminum cylinder, on one of the ends of which (radial type of housing) or on two ends of which (axial type of housing) contact pins are located. The terminals can be soldered or screwed.

The capacitance of electrolytic capacitors is measured in microfarads, and can range from 0.1 µF to 100,000 µF. The significant capacity of electrolytic capacitors, compared to other types of capacitors, is their main advantage. The maximum operating voltage of electrolytic capacitors can reach 500 volts. The maximum permissible operating voltage, as well as the capacitance of the capacitor, are indicated on its body.

This type of capacitor also has disadvantages. The first of which is polarity. On the capacitor body, the negative terminal is marked with a minus sign, it is this terminal that must be present when the capacitor is operating in a circuit at a lower potential than the other, or the capacitor will not be able to accumulate charge normally, and will most likely explode, or will in any case be damaged if left for too long keep it energized with the wrong polarity.

It is precisely because of polarity that electrolytic capacitors are applicable only in direct or pulsating current circuits, but not directly in alternating current circuits; electrolytic capacitors can only be charged with rectified voltage.

The second disadvantage of this type of capacitor is the high leakage current. For this reason, it will not be possible to use an electrolytic capacitor for long-term charge storage, but it is quite suitable as an intermediate filter element in an active circuit.

The third disadvantage is that the capacitance of capacitors of this type decreases with increasing frequency (pulsating current), but this problem is solved by installing a relatively small ceramic capacitor on the boards parallel to the electrolytic capacitor, usually 10,000 times less than that of the adjacent electrolytic capacitor.

Now let's talk about tantalum capacitors. An example would be K52-1 or smd A. They are based on tantalum pentoxide. The bottom line is that when tantalum oxidizes, a dense non-conducting oxide film is formed, the thickness of which can be technologically controlled.

A solid tantalum capacitor has four main parts: anode, dielectric, electrolyte (solid or liquid), and cathode. The production process chain is quite complex. First, an anode is created from pure pressed tantalum powder, which is sintered in a high vacuum at a temperature of 1300 to 2000°C to create a porous structure.

Then, by electrochemical oxidation, a dielectric is formed on the anode in the form of a film of tantalum pentoxide, the thickness of which is adjusted by changing the voltage during the process of electrochemical oxidation, as a result, the thickness of the film is only from hundreds to thousands of angstroms, but the film has such a structure that it provides high electrical resistance.

The next stage is the formation of an electrolyte, which is the semiconductor manganese dioxide. A tantalum porous anode is impregnated with manganese salts, then it is heated so that manganese dioxide appears on the surface; The process is repeated several times until complete coverage is obtained. The resulting surface is coated with a layer of graphite, then silver is applied to form a cathode. The structure is then placed into a compound.

Tantalum capacitors have similar properties to aluminum electrolytic capacitors, but they have their own characteristics. Their operating voltage is limited to 100 volts, the capacitance does not exceed 1000 microfarads, their own inductance is less, so tantalum capacitors are used at high frequencies, reaching hundreds of kilohertz.

Their disadvantage is their extreme sensitivity to exceeding the maximum permissible voltage; for this reason, tantalum capacitors fail most often due to breakdown. The line on the body of a tantalum capacitor indicates the positive electrode - the anode. Leaded or SMD tantalum capacitors can be found on modern printed circuit boards of many electronic devices.

For example, types K10-7V, K10-19, KD-2, are characterized by a relatively large capacitance (from 1 pF to 0.47 μF) with small sizes. Their operating voltage ranges from 16 to 50 volts. Their features: low leakage currents, low inductance, which gives them the ability to operate at high frequencies, as well as small sizes and high temperature stability of the capacitance. Such capacitors work successfully in DC, AC and pulsating current circuits.

The loss tangent tgδ usually does not exceed 0.05, and the maximum leakage current is no more than 3 μA. Ceramic capacitors are resistant to external factors, such as vibration with a frequency of up to 5000 Hz with acceleration up to 40 g, repeated mechanical shocks and linear loads.

Ceramic disk capacitors are widely used in smoothing filters of power supplies, in noise filtering, in interstage communication circuits, and in almost all electronic devices.

The marking on the capacitor body indicates its rating. The three numbers are deciphered as follows. If the first two digits are multiplied by 10 to the power of the third digit, the value of the capacitance of this capacitor in pf is obtained. So, a capacitor marked 101 has a capacity of 100 pF, and a capacitor marked 472 has a capacity of 4.7 nf.

For example, K10-17A or K10-17B, unlike single-layer ones, have alternating thin layers of ceramic and metal in their structure. Their capacity is therefore greater than that of single-layer ones and can easily reach several microfarads. The maximum voltage is also limited here to 50 volts. Capacitors of this type are capable, just like single-layer ones, of functioning properly in DC, AC and pulsating current circuits.

Capable of operating at high voltages from 50 to 15,000 volts. Their capacitance ranges from 68 to 100 nf, and such capacitors can operate in direct, alternating or pulsating current circuits.

They can be found in network filters as X/Y capacitors, as well as in secondary power supply circuits, where they are used to eliminate common-mode interference and absorb noise if the circuit is high-frequency. Sometimes, without the use of these capacitors, failure of the device can threaten people's lives.

A special type of high voltage ceramic capacitors - high voltage pulse capacitor, used for high-power pulse modes. An example of such high-voltage ceramic capacitors are the domestic K15U, KVI and K15-4. These capacitors are capable of operating at voltages up to 30,000 volts, and high-voltage pulses can occur at high frequencies, up to 10,000 pulses per second. Ceramics provide reliable dielectric properties, and the special shape of the capacitor and the arrangement of the plates prevent breakdown from the outside.

Such capacitors are very popular as loop capacitors in high-power radio equipment and are very welcome, for example, by Tesla manufacturers (for designing on a spark gap or on lamps - SGTC, VTTC).

For example, K73-17 or CL21, based on metallized film, are widely used in switching power supplies and electronic ballasts. Their housing made of epoxy compound gives the capacitors moisture resistance, heat resistance and makes them resistant to aggressive environments and solvents.

Polyester capacitors are available in capacities from 1 nF to 15 µF, and are designed for voltages from 50 to 1500 volts. They are distinguished by high temperature stability with high capacity and small size. The price of polyester capacitors is not high, so they are very popular in many electronic devices, in particular in ballasts for energy-saving lamps.

The capacitor marking contains a letter at the end indicating the tolerance for deviation of the capacitance from the nominal value, as well as a letter and number at the beginning of the marking indicating the permissible maximum voltage, for example 2A102J - capacitor for a maximum voltage of 100 volts, capacity 1 nf, permissible capacitance deviation + -5% . Tables for deciphering the markings can be easily found on the Internet.

A wide range of capacitances and voltages makes it possible to use polyester capacitors in direct, alternating and pulsed current circuits.

Polypropylene capacitors, for example K78-2, unlike polyester ones, have a polypropylene film as a dielectric. Capacitors of this type are available in capacities from 100 pF to 10 µF, and the voltage can reach 3000 volts.

The advantage of these capacitors is not only the high voltage, but also the extremely low dissipation tangent, since tanδ can be as low as 0.001. Such capacitors are widely used, for example, in induction heaters, and can operate at frequencies measured in tens and even hundreds of kilohertz.

Deserves special mention starting polypropylene capacitors, such as CBB-60. These capacitors are used to start AC asynchronous motors. They are wound with metallized polypropylene film onto a plastic core, then the roll is filled with compound.

The capacitor body is made of non-flammable material, that is, the capacitor is completely fireproof and suitable for operation in harsh conditions. The terminals can be either wired or terminal-mounted or bolt-on. Obviously, capacitors of this type are designed to operate at industrial network frequencies.

Starting capacitors are available for alternating voltages from 300 to 600 volts, and the range of typical capacitances is from 1 to 1000 microfarads.

Andrey Povny

Electronics use many different parts that together enable a range of actions. One of them is a capacitor. And within the framework of the article we will talk about what kind of mechanism this is, how it works, why a capacitor is needed and what it does in circuits.

What is a capacitor?

A capacitor is a passive electrical device that can perform various tasks in circuits due to its ability to accumulate charge and electric field energy. But the main range of applications is in filters for rectifiers and stabilizers. Thus, thanks to capacitors, a signal is transmitted between amplifier stages, time intervals are set for timing, and high- and low-pass filters are built. Due to its properties, it is also used for frequency selection in different generators.

This type of capacitor boasts a capacity of several hundred microfarads. Other members of the family of this electronics part are designed according to a similar principle. How to check the capacitor and make sure that the real state of affairs corresponds to the inscriptions? The easiest way is to use a digital multimeter. An ohmmeter can also answer the question of how to check a capacitor.

Operating principle and why a capacitor is needed

From the designation and schematic image we can conclude that even two metal plates located next to each other can act as a simple capacitor. Air will act as a dielectric in this case. Theoretically, there is no limitation on the area of ​​the plates and the distance between them. Therefore, even when spreading over vast distances and reducing their size, even if it is insignificant, some capacity is retained.

This property has found use in high-frequency technology. So, they learned to make them even in the form of ordinary printed circuit tracks, as well as simply by twisting two wires that are in polyethylene insulation. When using a cable, the capacitor capacity (µF) increases with length. But it should be understood that if the transmitted pulse is short and the wire is long, then it may simply not reach its destination. A capacitor can be used in DC and AC circuits.

Energy storage

As the capacitor capacity increases, processes such as charge and discharge proceed slowly. The voltage across a given electrical device increases along a curved line, which in mathematics is called an exponential. Over time, the capacitor voltage will increase from a value of 0V to the level of the power supply (if it does not burn out due to too high values ​​of the latter).

Electrolytic capacitor

At the moment, electrolytic capacitors boast the highest specific capacitance in terms of the ratio of this indicator to the volume of the part. Their capacity reaches values ​​of 100 thousand microfarads, and the operating voltage is up to 600 V. But they work well only at low frequencies. What is this type of capacitor used for? The main area of ​​application is filters. Electrolytic capacitors are always connected to circuits with correct polarity. Electrodes are made from a thin film (which is made of metal oxide). Since a thin layer of air between them is not a good enough insulator, a layer of electrolyte is also added here (concentrated solutions of alkalis or acids act as it).

Supercapacitor

This is a new class of electrolytic capacitors called ionistors. Its properties make it similar to a battery, although certain limitations apply. Thus, their advantage lies in the short charging time (usually a few minutes). What is this type of capacitor used for? Ionistors are used as backup power supplies. During manufacturing, they turn out to be non-polar, and where is plus and where is minus is determined by the first charge (at the manufacturing plant).

Temperature and rated voltage have a significant impact on performance. So, at 70˚C and 0.8 power will give only 500 hours of operation. By reducing the voltage to 0.6 of the nominal value and the temperature to 40 degrees, its service life will increase to 40 thousand hours. You can find ionistors in memory chips or electronic watches. But at the same time, they have good prospects for their use in solar batteries.